Convertible Notes (Details 3) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Interest expense related to notes
Amortization of discount and debt issuance costs			$ 3,379	$ 5,396
Interest expense	$ 2,534	$ 4,634	4,805	9,055
1.125% Convertible Senior Notes due 2018
Interest expense related to notes
Interest	0	228	0	281
Amortization of discount and debt issuance costs	0	1,106	0	2,197
Convertible Notes Payable [Member]
Interest expense related to notes
Interest expense	$ 2,294	$ 3,537	$ 4,565	$ 6,863
Convertible Notes Payable [Member] \| Senior, One Point Three Seven Five Percent Convertible Notes Due Two Thousand Twenty Three [Member] [Member]
Interest expense related to notes
Convertible notes stated interest rate (as a percent)	1.375%	1.375%	1.375%	1.375%
Debt Instrument, Interest Rate, Effective Percentage	4.90%	4.90%	4.90%	4.90%
Convertible Notes Payable [Member] \| 1.125% Convertible Senior Notes due 2018
Interest expense related to notes
Debt Instrument, Interest Rate, Effective Percentage		5.50%		5.50%
Convertible Senior Notes \| Senior, One Point Three Seven Five Percent Convertible Notes Due Two Thousand Twenty Three [Member] [Member]
Interest expense related to notes
Interest	$ 593	$ 593	$ 1,186	$ 1,186
Amortization of discount and debt issuance costs	$ 1,701	$ 1,610	$ 3,379	$ 3,199
Convertible Notes Payable [Member] \| 1.125% Convertible Senior Notes due 2018
Interest expense related to notes
Convertible notes stated interest rate (as a percent)		1.125%		1.125%

Amount of amortization expense attributable to debt discount (premium) and debt issuance costs.

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